I have an new Apple iPod that replaces my Dell Jukebox mp3 player.?

How do I get all of my songs from my pc's Media Player (they're in .wma format) converted to .mp3's so I can put them on my new iPod. I have roughly 1300 songs, some from cd's I own, so they're re-rippable (if I HAVE to) but a lot are from Napster at $.99 a pop. I really don't want to lose all this media. I picked out the iPod because of all the accessories that are available, that weren't offered for my old Dell Jukebox.